Louis' swallowwort is native to Europe, and may have
been introduced intentionally for ornamental purposes or
imported unintentionally on other plants or materials.
Louis' swallowwort occurs in the northeastern and
mid-Atlantic states to the Midwest, and in California,
where it threatens native flora in fields, forest edges,
woods and open disturbed areas. It grows vigorously and
densely, blocking light from reaching the plants it
scrambles across, often leading to their death.
Swallowwort spreads vegetatively and by seeds dispersed by
the wind. Because there are many native milkweed species
in the United States, correct identification of this plant
is imperative.

Prevention and Control
Do not plant this or other exotic swallowworts. Plants can
be pulled by hand or mowed, once or twice per season, or
dug up, removing the entire crown. Picking of pods is used
as a last resort to help prevent production and spread of
seeds. Application of systemic herbicides like glyphosate
and triclopyr is also effective.